It is known that the life and performance of new and existing pipelines can be extended and optimised by lining lengths of metal pipe with polymer liners. For example, the Applicant's Swagelining® pipe lining service allows existing pipelines to be remediated and new pipelines to be provided with corrosion resistance by installing a polymer liner that remains in tight contact with the inside of a host pipe.
To join adjacent lined pipe lengths, it is known to provide an electrofusion fitting to connect the inner pipe linings prior to welding the metal pipe lengths together. The Applicant's earlier International Application Publication Number WO 2010/041016, FIG. 1 of which is reproduced in part in FIG. 1 of the present application, discloses an electrofusion fitting 101 and a method of forming a pipe joint between two lined metal pipe lengths 103a,103b incorporating such a fitting 101. The electrofusion fitting 101 is a sleeve largely comprised of a thermoplastic material and includes heating coils 107a,107b disposed at either end of the fitting 101. In use, the lining 105a is stripped back and the electrofusion fitting 101 inserted into the end of metal pipe length 103a. The heating coils 107a are then provided with electrical power which causes the fitting 101 and the lining 105a in the vicinity of the coils to melt and fuse together. The process is repeated to fuse the fitting 101 to the lining 105b of the other metal pipe length 103b, after which the metal pipe lengths themselves 103a,103b are welded together at 109.
While the effect is such that a very effective weld is formed between the fitting 101 and the pipe linings 107a,107b, it is difficult to ensure that the fusing process can be consistently repeated.
Accordingly, it is an object of at least one aspect of the present invention to provide a method of joining sections of lined pipe using an electrofusion fitting that provides repeatable results. Embodiments of aspects of the present invention are intended to realise this object and to obviate or mitigate one or more further disadvantages of existing electrofusion fitting methods.
Further aims and objects of the invention will become apparent from reading the following description.